As is well known in the prior art, image projection systems focus signal information to selected regions of a display screen to produce images. For example, in a conventional cathode ray tube ("CRT"), a beam emitted from an electron gun is directed to a small cross section on a luminescent screen and is varied in position and intensity to produce a visible pattern. As the size of the display screen increases, however, it becomes more and more difficult to accurately focus the electron beam to a specific area of the screen because of the increased size and volume of the CRT associated with the larger screen. To overcome this problem, it is also known to attach a so-called image transfer device to the display screen to magnify the screen image, thereby obviating an increase in the CRT dimensions. Typically, the transfer device comprises a plurality of optical fibers assembled into a bundle such that an image at a first or input end thereof (i.e., the image on the display screen) can be projected there through, for viewing, at a second or output end thereof. One such light transfer device is shown in U.S. Pat. No. 3,043,910 to Hicks, Jr. The display portion of the Hicks, Jr. device is manufactured by stacking a plurality of discrete fiber optic ribbons in spacer strips at a predetermined angular relationship and then cutting the strips along a bias thereof.
Fiber optic image transfer devices of the type described in the Hicks, Jr. patent have certain limitations that have prevented their widespread use for large screen display applications. The most significant operational problem in such devices is the tendency of each fiber optic ribbon to "skew" or twist with respect to the other ribbons, thereby causing the image displayed at the second end of the device to have severe vertical discontinuities. U.S. Pat. No. 4,650,280, to Sedlmayr, issued Mar. 17, 1987, and assigned to Advance Display Technologies, Inc., describes a unique image transfer device and manufacturing technique therefor for overcoming this problem through rigid alignment of the fiber optic ribbons in spacers in three mutually perpendicular planes at both ends of the device. A display device manufactured in accordance with the teachings of U.S. Pat. No. 4,650,280 transfers an aesthetically-pleasing image between the input and output of the device with high resolution.
Despite the significant operational improvements in fiber optic image transfer devices provided by the teachings in the Sedlmayr patent, it remains desirable to produce such devices without the use of discrete optical fibers. One such device is shown in U.S. Pat. Nos. 3,391,969 and 3,498,864 to Ogle which describe a fiber optic article and method of manufacture wherein planar fiber optical sheets are formed with elongated grooves filled with light transmitting material. The optical sheets are joined together with the grooves in confronting relation to form a fiber optical array. Although the Ogle manufacturing technique obviates the use of discrete optical fibers, the resulting fiber optic device does not adequately transfer an image between the input and output ends thereof. This is because each planar fiber optical sheet formed in the Ogle manufacturing technique has the same thickness between the input and output ends of the device. When the optical sheets are joined together to form a fiber optical array, there are discrete areas on the input end of the device which contact elemental portions of the image to be transferred but which have no corresponding display areas on the output end of the device. Therefore, information in the image is lost as the image is transferred between the input and output ends of the device.
There is therefore a need for an improved image transfer device which overcomes these and other limitations associated with the prior art.